1. Field
The embodiments described below relate generally to radiotherapy. More particularly, some embodiments concern determination of neutron doses resulting from radiation and/or particle therapy.
2. Description
Linear accelerators and particle accelerators generate treatment beams used for patient therapy. At high energies, interactions between a treatment beam and heavy matter within a treatment room (e.g., flattening filters, electron target, collimator, shielding) result in the generation of neutrons. These neutrons may adversely affect a patient to which the treatment beam is delivered. Accordingly, it is desirable to measure neutrons generated within a treatment room.
Conventional active neutron dosimetry devices (e.g., 3He proportional counters) are not suitable for the above-mentioned measurement. For example, high energy x-ray leakage fluence generated by a treatment beam is significantly greater than any generated neutron fluence and distorts the measurement thereof. Moreover, high intensity pulsed photon fluences generated by conventional linear accelerators result in neutron counts which correspond to accelerator pulse rates rather than actual neutron fluence. It has been suggested to address the foregoing phenomena by placing active counters outside of a treatment room. Dose determinations based on such placement are not suitably accurate for many applications due to the vague and tenuous relationship between neutron fluence outside a treatment room and neutron dose at a target or other location within the treatment room.
Passive detectors may therefore be employed to detect neutrons generated within a treatment room. Conventional passive detectors include gold foil activation detectors, thermoluminescent dosimeters and superheated bubble emulsions. Each of these passive detectors may be deployed with or without a moderating envelope such as a Bonner sphere. Although passive detectors might not suffer from the above-mentioned deficiencies of active detectors, the time and effort required to analyze a detector after neutron exposure and to determine a neutron dose is unsuitable for efficient verification and/or monitoring of radiotherapy.